Refining of liquid copper

ABSTRACT

A process for refining copper comprises removing anionic impurities by electrolytic or chemical reaction followed by removing the remaining impurities by contacting molten copper with a fluorine containing salt.

United States Patent 72 inventor Phlllp E. Lapat [501 Field of Search .I204/39. Sudbury,Mm. 106-108, 128, I29, 59, 60, 140, 64; 75/76 [2| App].No. 841,629 221 Filed July 14,1969 1 References Cited [45] Patented Oct.26, 1971 UNITED STATES PATENTS I 1 Assisnee Kennwm w" fiorwmbn 2,347,4504/1944 Young 204/64 R New York, NY. l,964,906 7/1934 Chandler et al.204/64 R 502,43l 8/1893 Eames 204/64 R Primary Examiner-John H. MackAssistant Examiner-R. L. Andrews 5 0F Attorneys-John L. Smado and LOWC"McCarter 22 Claims, 1 Drawing Fig.

[52] [1.8. CI 204/140, ABSTRACT: A process for refining copper comprisesremov- 204/64, 204/106. 204/l29 ing anionic impurities by electrolyticor chemical reaction fol- [51] Int. Cl CZZd 3/14, lowed by removing theremaining impurities by contacting C0 lb molten copper with a fluorinecontaining salt.

p 3 3, r We COPP IMPURII'Y REMOVAL ELECTROLYTIC Homo 0R COPPER CHEMICALMETALLIC OMPURITY l mzuovm. moms ELECTROLYTIC P IMPURITIES 0R LIQUIDSKET caemcm. "$8 MAKEUP CAST'NG FUSEO SALT RECYCLE USED SALT CONTAIMNGIWURlTY METAL FLUGQIMS FUSED SALT PURIFICATDN IMPURITY METAL PATENTEHUET2 6 I971 K53 ANIONIC CQPPER IMPURITY REMOVAL ELECTROLYTIC UQU) 0R COPPERCHEMICAL 1 METALLIC IMPURITY l REMOVAL AN'ON'C ELECTROLYTIC PURElMPURITIES 0R g flg CHEMICAL FUSED TO sALT q A CASTING MAKEUP 22aRECYCLE FUSED SALT CONTAINING IMPURITY METAL VFLUORIDES FUSED SALTPURIFICATION IMPURITY' METAL FLUORIDES INVENTOR Philip E. Lopot ATTORNEYREFINING OF LIQUID COPPER BACKGROUND OF THE lNVENTlON Copper refining isconventionally practiced upon impure TABLE II. Impurity Analyses ofCopper Anodes 1 z .1 4 copper from three sources. These comprise l)flotation con- 5 centrates, generally copper-iron sulfides, (2)"precipitate" copper obtained by cementation with scrap iron fromaqueous on solutions produced by leaching of mine waste dumps, and (3) Sd ra co er Sources l) and (2) ass throu h a (L04 secon ary orsc p pp P 8'0 T, 0.021 0.013 0.016 well-established smelting and convertingprocess, whose end in 0.14 0.011 0.031 0044 product is an impure gradeof metal known as "blister B Mil 06 copper." Source (3) may enter therefining process directly, 3: 1" "3 23:7 3-3: or it may first be smeltedin a blast furnace, whose impure 0.033 Mm product metal is known asblack copper." Table 1 below 5 0.05 0.0001 0.020 0.0m gives analyses ofa number of samples from various copper sources.

TABLE L-ANALYSES 0F CRUDE COPPERS Weight percent Mlsc. copper Blistercopper-s Black coppers scrap .34 1.03 .26 .062 .014 .069 .030 .030 .030.0012 .000s .040 032 035 16 .0039 .0062 .0031 .0005 .27 .010 .00025.00014 .00048 .002: .10 ND. .0004 .020 ND. .00027 .00021 .0012

. Balance Balance Balance Balance Conventional refining is done byeither Fire Refining or Electrolytic Refining.

Fire Refining comprises (1) transferring the crude liquid copper to arefining furnace (or melting it in that furnace should it arrive fromthe smelting process in solidified form). (2) oxidizing the molten metalby introduction of air through iron blowpipes, (3) frequently skimmingslag from the surface of the bath, and (4) reducing or poling" the metalwhich consists of inserting green hardwood poles into the molten metalbath that decompose into hydrocarbon gases and carbon. The refinedcopper is then ready for casting into desired shapes.

Fire refining is capable of removing substantially all of the sulfur.zinc, tin and iron, and partially removing several other impurities.Nickel, bismuth, selenium and tellurium, on the other hand, resist firerefining treatments almost completely.

The refining of a BOO-ton charge of blister copper requires about 20hours; charging time consumes 2 hours, melting and skimming l4 hours,oxidizing llfi hours and reducing 2% l-ours. Subsequent casting consumes3% hours, so that the entire process operates on a 24-hour cycle.

Electrolytic Refining is used only where the amount of precious metalsor the character of the impurities present in the crude copper warrantthis expensive refining method. The first process step is fire refiningmuch as described above, except that the tire refining is carried onlyfar enough to permit casting of economically acceptable anodes.

The second process step is casting anodes by tapping the metal in acontinuous stream into a casting ladle and bringing molds to the pouringposition under the ladle. The usual casting machine has from 16 to 28copper molds oriented horizontally at the periphery of a wheel.Solidified anodes are mechanically or pneumatically raised forengagement of a tong under the anode lugs, and then transferred tocooling tanks. They are inspected, and trimmed where necessary withpneumatic tools for removal of edges and fins. Anodes typically havedimensions 36 inches wide X 39 inches long X Hi inches to 2 inchesthick, and weigh between 500 and 800 pounds. Table ll below gives somerepresentative impurity analyses of copper anodes:

In the third process step, the anodes are suspended, along with purecathode starting sheets, in electrolytic cells containing sulfuric acidand copper sulfate and copper is electrolytically transferred from anodeto cathode over a period of 25 to 3| days. Impurities dissolve and arecarried away in the recirculating electrolyte, or else fall to thebottom of the cells as solid particulate "anode mud or "slimes.Electrolysis cannot be carried to completion because anodes do notdissolve uniformly; ID to 20 percent of the anode becomes scrap which isrecycled to the fire refining furnace. Additionally, about I percent ofthe anode is converted to anode mud or slimes." This material is treatedseparately for recovery of Cu, Se, Te and the precious metals.

in a fourth process step. the cathodes are melted so that they may becast into desired commercial shapes. Cathode melting should rationallybe confined to bringing solid cathodes into the molten state undernoncontaminating conditions with provision for elimination of the smallamounts of sulfur and occluded gas which may be introduced with thecharge. However, in reverberatory furnace practice, because ofcontamination from combustion gases and iron pickup from furnace pipeand rabbles, melting of cathodes requires essentially the same procedureas for fire-refining of impure copper. It is a batch process and everyeffort is made to perform the complete cycle in 24 hours.

OBJECTS OF INVENTION It is the principal object of the present inventionto provide an improved process for purifying copper. It is a furtherobject of the present invention to provide a rapid, effective, and lesscostly method for purifying copper. Another object is to provide forremoving substantial amounts of impurity elements including but notlimited to oxygen, sulfur, selenium, tellurium, nickel, iron, lead,bismuth, arsenic, antimony, tin, phosphorus, zinc, cadmium and hydrogen.Yet another object of the present invention is to decrease theconcentrations of the aforementioned impurities to very low levels, suchthat the product copper is equal or superior in purity to conventionallyrefined copper. The process of the present invention possesses severaladvantages over the prior art. One of these is that the process isconducted entirely at high temperature upon liquid copper, therebyeliminating the conventional unit operations of casting anodes andmelting cathodes. Another advantage is that impurities are transferredout of the copper, rather than transferring copper away from theimpurities as in conventional electrolytic refining. Since the quantityof impurities in crude copper is ordinarily about 1/l00 of the totalweight, the necessary residence time in the apparatus is therefore verymuch shortened, as from 32 days to a few minutes. Another advantage isthat there is no anode scrap, which ordinarily constitutes l-20 percentof the copper, and which must be recycled to the anode furnace becauseit is physically impractical to electrolyze an anode completely. Anotheradvantage is that the refinery will be smaller and less costly to build,because the process of the present invention (l has only two stepsinstead of the four steps of conventional electrolytic refining, and (2)the steps are much more rapid than conventional electrorefining. Anotheradvantage is that operating costs will be smaller for the same tworeasons.

Further objects and advantages of the present invention will appearhereinafter.

SUMMARY OF THE lNVENTiON in accordance with the process of the presentinvention, it has now been found that the foregoing objects andadvantages may be readily accomplished by an improved process forpurifying copper by providing molten copper, removing the anion formingelements. i.e., oxygen, sulfur, selenium, and tellurium, by making theimpure molten copper the cathode of an operating electrolytic cellcontaining a fused salt electrolyte and an insoluble anode, transferringthe anion-free copper from the electrolytic cell to a chemical reactor,removing the metallic impurities by contacting the molten copper withone or more fluorine-containing compounds in a chemical reactor andremoving the purified copper from the reactor.

Altemately, anion impurity elements can be removed by contacting impurecopper with a molten salt or a mixture of molten salts containingdissolved reactive metal, in a chemical reactor, and removing theanion-free copper to the second process step.

Metallic impurity removal can also be accomplished by providing copperfree of anionic impurity elements from a first process step, and makingthis copper the anode of an electrolytic cell containing a fused saltelectrolyte bearing fluorinecontaining compounds, and removing thepurified copper from the electrolytic cell.

The anion impurity elements and the cation or metallic impurities may besimultaneously removed electrochemically in a two compartmentelectrolytic cell having a common receptacle or container for the impureliquid copper and separate compartments for two electrolytes.

DESCRIPTION OF THE DRAWING The accompanying drawing illustrates anidealized flow diagram for the process of the invention describedherein.

PREFERRED EMBODIMENTS First Step In the first step of the process ofthis invention the anionic impurities are removed by electrolytic orchemical reaction. In the electrolytic method the impure liquid copperis made the cathode of an electrolytic cell containing a fused saltelectrolyte and an insoluble anode. The electrolyte composition incathodic refining is not highly critical, but is conveniently chosenfrom among the alkaline earth chlorides or fluorides or mixtures thereofbecause of their relatively low volatility near the melting point ofcopper, their chemical stability and their compatibility with graphiteand certain other conventional oxide refractories. Alkali metal halidesmay also be added to the electrolyte composition. The alkali metalhalides may comprise from about 0.3 weight percent to about [0 weight 5are removed by an electrode reaction taking place at thecathode-electrolyte interface. The reaction may be represented as: Cu,S(dissolved in metal phase) +2e-+ 2Cu( l +S {transferred to the saltphase) where oxygen, selenium and tellurium also act after the manner ofsulfur.

The effectiveness of the removal of the anionic impurities isdemonstrated in example I.

EXAMPLEl 487 grams of impure copper having an initial composition asshown in table I]! was melted along with l2) grams of anhydrous bariumchloride electrolyte in an alumina crucible. The alumina crucible itselfwas contained in a large graphite crucible, a portion of whose sidewallwas in contact with the electrolyte, and which served as the anode. Thecathode cur rent lead was a graphite rod extending down into the copperpool, and insulated from the electrolyte by an alumina sheath. The cellwas maintained at l,l50 C. in an inert atmosphere, and electrolysis wasperformed at 3.3 volts with a cathode current density of [.0 amps. persquare centimeter. The average analysis of the impurities in the copperbefore and after electrolysis is shown in table lll.

Since the use of a graphite rod electrode results in oxygen removal bychemical as well as electrochemical reaction, this example is primarilya demonstration of S, Se, Te removal.-

Oxygen, however, has been found to behave similarly.

It is necessary in the case of oxygen removal experiments to determine,by comparison with control experiments in which the salt and metal arebrought into contact under identical conditions (except that no electriccurrent is passed), how much deoxidation is attributable to chemicalreaction with carbon. The difference between this and the totaldeoxidation in a cathodic electrolysis experiment may be ascribed toelectrolysis. Table IV contains examples of control experiments on allanionic impurities, and two electrolytic experiments which followbehavior of oxygen content:

TABLE 1\' Composition, welglit percent Current Element passed observedInltial Final I). 58 (l. 46 92 7B B4 66 0. ll 065 0. ll 001 l. 5 23 l. 5OOl An examination of tables Ill and IV reveals that the electrolysiscompletely removes the anionic impurities. oxygen, sul- 5 fur, seleniumand tellurium, but has limited or no effect on the metallic impuritiesln order to prevent impurity buildup and thus give the processcontinuity, the effect of the electrolyte upon the anode reaction mustbe considered. If the electrolyte is chloride-based and the solubilityof chalcogenides is slight, as depicted in example I above. the majoranode product may be chlorine. The overall cell reaction becomes of thetype:

Cu,$ (in liquid Cu )+BaCl, Bas+Cl,(g)+2Cu( l) l and the electrolytebecomes fouled with oxygen, sulfur, selenium. and tellurium in the formof barium compounds. In some cases where the electrolyte is aninexpensive and impure salt to begin with, the electrolyte can bediscarded when contaminated and sold for a rioncritical use. i havecalcium chloride especially in mind for this route.

A second method for dealing with the contaminated electrolyte dependsupon the low solubility of the chalcogenide compounds in the alkalineearth chloride electrolytes. A portion of the electrolyte iscontinuously withdrawn from the electrolytic cell. cooled slightly toprecipitate the chalcogenide compounds which are then mechanicallyseparated by high-temperature filtration or its equivalent. The purifiedelectrolyte is then reheated and returned to the electrolytic cell.

Another. and the preferred method is to prevent impurity buildup byusing a fluoride based electrolyte in which chalcogenide compounds aresignificantly soluble. They may be soluble as copper compounds, impuritycompounds. or compounds with the metal ions of the electrolyte, such asBaS, BaO. etc. Their presence may be due to simple solubility, to theformation of complex species or to reaction products.

The concept to be exploited is that the anode reaction may beadvantageously confined to discharging chalcogenide-bearing ions becausethe decomposition potential for chalcogenide compounds in theelectrolyte is generally smaller than that for equivalent halides, andespecially fluorides.

Standard Decomposition Potentials for Alkaline Earth Compounds at LIOOC. (volts) The difference in decomposition potentials is so large thatthermodynamic activity effects due to complexing or dilution will notalter the deposition potentials of chalcogenides to a critical degree.

Thus. oxygen. sulfur, selenium and tellurium will be discharged at theanode and the cell is essentially self-cleam ing, the overall cellreaction being of the type:

A significant feature of the cathodic electrolysis is that whenperformed at constant current, the cell voltage is a function of theimpurity concentration. and the cell voltage rises markedly as the endpoint of the reaction is approached. By limiting the available voltagethrough the cell. it is practicable to halt the reaction before thedecomposition potential of the electrolyte is reached. In this waycontamination of the purified copper by calcium, magnesium or otherreactive metals derived from the electrolyte is avoided.

In the practical sense, a process conducted according to Reaction l issimply the desulfidation (or deoxidation. etc.) of copper by bariummetal. and the use of the electrolytic cell may be viewed mainly as aconvenient way to prepare barium metal and perform a reaction with it.Also, the barium metal will have been produced with less energyexpenditure than if pure barium metal had been separately prepared.

The potential advantages of operating Cathodic Refining according toReaction (2) rather than Reaction (I) include avoidance of problems ofdisposal of the chalcogenide com pounds e.g., BaS. BaO, Base, BaTe). sothat an electrolyte purification circuit is unnecessary; the opportunityto recover Se and Te by condensation of the anode gas. and eliminationof chlorine gas recycling (as by using it to chlorinate the chalcogenidecompounds and regenerate BaCl An advantage of using reaction l ratherthan Reaction (2) is that it can be performed in a chemical reactorwithout electrodes. as well as in an electrolytic cell. This is becausemany of the reactive metals are extensively or completely miscible withtheir halides, forming true liquid solutions at the temperatures wherecopper is molten. It thus becomes unnecessary for the liquid copper toremain in electrical contact with an electrode. instead, the copper canbe broken into small droplets and permitted to settle by gravity througha salt-filled vessel or contacting column. so that the reaction surfacearea of the copper droplets per unit area of plant floor space is muchlarger and the required plant size appropriately smaller than if anelectrolytic cell is employed.

For example. if droplets of liquid copper 5 mm. in diameter areuniformly dispersed in a cylindrical salt-filled column 6 feet indiameter X 8 feet high. and the distance between droplets is 2 cm.. thetotal surface area presented by the droplets is 904 it. if the columnwith ancillary equipment occupies a floor space 8 ft.)( 8 ft.. thenthere are 14.! ft. of reaction interface per ft of plant floor space.

This figure is compared below with electrode areas typically encounteredin existing commercial electrolytic processes:

Cu in the salt column described above.

it is seen that a high-temperature electrolytic cell having a singleliquid pool electrode. horizontally oriented. has an inherently smallelectrode area per unit area of plant floor space. and thus may notminimize the plant size or its capital cost as effectively. Stacking ofliquid pool electrodes is possible. to achieve a denser configuration ofelectrode surfaces as in aqueous electrolysis with vertical. solidelectrodes; but this obviously requires more sophisticated constructionwhich may offset the capital cost savings for which it is responsible.

Two further advantages of the chemical reactor version of the anionremoval process derive from the fact that in this version the productionof reactive metal (such as Ca. Ba. Mg, Na. etc.) dissolved in its halidesalt is distinct and separate from its utilization in refining.Therefore l the reactive metal may be purchased instead of manufacturedby the copper refinery, and (2) the optimal values of process parametersfor manufacturing reactive metal, should the copper refinery choose toundertake it. will in general be different from those prevailing in thecopper refining operation; separation of the two functions may thereforepermit each to be performed under its most favorable circumstances.

in the removal of chalcogenide impurities by chemical reaction asdescribed above. reaction products accumulate in the molten salt. Ingeneral their solubilities in the molten salt are believed to be quitelimited. and they will be precipitated. The densities of compounds ofreactive metals with chalcogenide elements in general lie between thatof the molten salt and that of liquid copper. The solid compounds willtherefore be trapped by gravity just above the interface between themetal and salt layers and can be removed from the system by gravitythrough a separate taphole located near the interface. The

solid compounds will be admixed with salt. It may or may not be usefulto separate the admixed salt, depending on whether or not the Sc, Te andsalt are to be recovered.

ln judging the merit of the chemical reactor method for anion removal asheretofore described, a comparison naturally arises with conventionaldeoxidation processes wherein a reactive metal such as lithium orcalcium is added directly to molten copper as a deoxidizer. The use of asolution of reactive metal dissolved in its halide is advantageous inthat it provides a physical contacting process of the reagent with thecopper which will be more uniform, controllable, safe and efficient thanone employing reactive metal alone.

Second Step In the second step of the process of this invention theremaining base impurity elements such as nickel, iron, lead, bismuth,arsenic, antimony, tin, zinc, cadmium, and phosphorus are removed bysubjecting the molten copper either to a chemical refining reaction orto an electrochemical refining reaction in which a copper fluorideequivalent is the reactive substance employed.

y The following definitions will aid in the understanding of theinvention as described hereinafter in the specification and in theinterpretation ofthe appended claims.

The term CuF," is defined for the purposes of this application as amolten solution of stoichiometric cupric fluoride, or CuF,, which hasbeen saturated with, or is in chemical equilibrium with, molten coppermetal.

A measure of the ability of CuF, to perform fluorinating reactions isdefined by its free energy of dissociation; which is the free energychange of the reaction:

(Zlx )CuF,@( 2/x )Cu+F,(g) (3) This may be more CuF,stated byconsidering the dissociation reaction to be CuFJ Cu-i-F, (4)

for which the standard free energy change is approximately known, andaccounting for the stoichiometric difference between CuF, and CuF, bymeans of an activity term which uses CuF, as a standard state:

(ac-i) (PF-2) CuFg) where AG is the Gibbs free energy change, and a anda p denotes activities at saturation.

The term "fluorine potential," or p,,, is another measure of the abilityof CuF to perform fluorinating reactions. It is defined for the purposesof this application as the partial pressure of fluorine gas produced asa thermodynamic consequence of a chemical reaction equilibrium. Forexample, in a system at a defined temperature, containing CuF, and Cu inmuch larger quantity than all other reactive substances, such asimpurity metals. the fluorine potential is essentially fixed by thepresence of the major constituents, i.e., copper and CuF,. It is definedby the equilibrium constant for reaction (3):

AG 4)=AG i +RTln calories.

3 ean) in this example a and a are not expected to vary significantlyfrom unity, so that K zp ntm.

The term copper fluoride equivalent" is defined for the purposes of theapplication not simply as stoichiometric cupric fluoride having theformula CuF,, but more broadly as any product or mixture of productshaving an ability to perform fluorinating reactions upon liquid copperand the impurities contained therein which is controlled or limited bythe thermochemical properties of molten CuF,. Thus "copper fluorideequivalent is any substance which upon contact with liquid copperprovides a fluorine potential P at least as great as does CuF,. Statedanother way, copper fluoride equivalent is any fluorine-bearing compoundthat is thermodynamically less stable than CuF, and consequently willact as a fluorinating agent for liquid copper and the impurity elementstherein. Thus, elemental fluorine gas introduced into molten copper inlimited or small quantity, relative to the amount of copper, reacts toform CuF, and is therefore termed copper fluoride equivalent" as definedabove.

Similarly, elemental fluorine gas introduced into a molten fluoride saltsolution which contains a nonstoichiometric fluorine compound such asCuF,, or a stoichiometric fluorine compound capable of accepting morefluorine to become a stoichiometric fluorine compound of higher valence,which is in contact with molten copper, the quantity of such fluorinegas being small or limited relative to the amount of molten copper,reacts with the nonstoichiometric fluorine compound or stoichiometricfluorine compound capable of accepting more fluorine to become astoichiometric fluorine compound of higher valence in the salt to formCuF, where x y 2 CuF, in turn reacts with molten copper to form moreCuF,. The process is thus an indirect fluorination of copper via thesalt phase termed copper fluoride equivalent" as defined above.

Similarly, a high-valency fluorine compound which readily gives up apart ofits fluorine content to molten copper, reverting in the processto a fluoride compound of lower valency, is termed copper fluorideequivalent. An example is antimony pentafluoride, which may reactaccording to:

Stannic Fluoride (SnF is another example of a "copper fluorideequivalent. Stannic fluoride readily gives up part of its fluorine underthe conditions of refining liquid copper to become stannous fluorideISnF Stannic fluoride is particularly adaptable to the process of thisinvention since it is a solid at room temperature, and yet sufficientlyvolatile at liquid copper temperatures so that it does not remaindissolved in the molten copper or the molten salt.

The majority of fluorine containing compounds are not termed "copperfluoride equivalent" because they are thermodynamically more stable thanCuF, and cannot act as fluorinating agents for copper.

Another method of defining "copper fluoride might have taken thespecific term cuprous fluoride, or CuF, into account and described thecomposition CuF, in terms of a mixture of CuF,+CuF, or CuF-iCu,depending on the numerical value of x. There is however no good reasonat the present time to invoke this additional complication innomenclature, since the neutral compound CuF has not yet beencharacterized, or even proved to exist, either in gaseous or condensedform, at any temperature. Nevertheless, the definition of CuF, which hasbeen adopted as an adequate formalism for purposes of this applicationshould not be construed to mean that CuF does or does not exist, or thatCuF species do or do not participate in the process of the presentinvention.

Cupric hydroxy fluoride [Cu(0H)F] is thought to be capable ofapproaching the performance I have observed with the copper fluorideequivalents as described herein. It is believed that under certainprocess conditions the use of cupric hydroxyfluoride could be consideredan adequate substitute for CuF,.

Utilization of a copper fluoride equivalent to refine molten copper bychemical reaction may be brought about in any ofa number of ways.

I. Copper fluoride as anhydrous CuF, may be brought into direct contactwith molten copper in the chemical reactor.

2. Copper fluoride may be prepared by reacting or burning elementalfluorine gas and anion-free impure copper in a torch or high-temperaturereactor. The reaction or combustion products-copper fluorideequivalent-are then brought into contact with molten copper in thechemical reaction vessel.

3. Carbon and fluorine gas may be reacted as by contacting fluorine gaswith charcoal. The reaction gases comprising principally CF C F Cal andCI, are then passed through the molten copper where the gases decomposeand the fluorine combines with copper to form the copper fluorideequivalent.

4. A portion of the reaction products of (3) above comprise cyclicfluorocarbon compounds which are liquid at room temperature. such asCyclo-C F Cyclo-C F and Cyclo-C-,F,.. This liquid mixture may bevaporized by heating, and then passed through the molten copper wherethe vapors decompose and the fluorine combines with copper to form thecopper fluoride equivalent. 10

5. A copper fluoride equivalent such as antimony pentafluoride orstannic fluoride may be introduced into the molten copper in anyconvenient manner. This procedure is especially suitable becauseantimony pentafluoride. antimony trifluoride, stannic fluoride andstannous fluoride are all volatile enough so that they evaporate bothfrom the molten copper and salt phase. and do not accumulate. Antimonypen tafluoride is a liquid and stannic fluoride is a solid at room.temperature and can be conveniently handled.

6. It has been found that the copper fluoride equivalent need not beused at full strength. but may be dissolved in various other stable saltsolvents such as alkaline earth fluoride eutectic mixtures. In somecases a salt containing very little dissolved copper fluoride equivalentmay be adequate, de-

pending upon which impurities are to be removed and to whatconcentrations they must be reduced.

One of the advantages of using a copper fluoride equivalent in dilutedform is that if the copper fluoride is largely consumed in the refiningreaction it would appear to be feasible to repurify the salt phasecontaining the copper fluoride and the impurities by fused saltelectrolysis in which the residual copper fluoride and then the impuritymetal fluorides will decompose preferentially at the electrodes becausethey are thermodynamically less stable than the salt solvent. A secondadvantage is that the use of a diluent material may permit sup pressionof electronic conductivity thought to exist in coppersaturated liquidcopper fluoride, which would greatly reduce current efficiency inelectrolytic purification of the impurity laden fused salt. A thirdadvantage is that the constituents of the salt phase may be chosen so asto depress the thermodynamic activities of specific impurity fluoridesand so drive specific refining reactions further toward completion thanotherwise possible. It has been found that as little as l mole percentcopper fluoride in the electrolyte will be capable of refining liquidcopper where the impurity level is low.

In the electrochemical method of performing the fluoride refiningreaction an electrolytic cell is used rather than a chemical reactor.The major constituents of the electrolyte should be very stablethermodynamically (for example.

CaF,-Mgl-'B2). nonvolatile. and liquid at temperatures substantiallybelow the melting point of copper. The electrolyte should also contain asmall concentration of copper fluoride.

In the electrolytic cell there will be an impure liquid copper anodepool and a pure copper cathode pool. Electrolysis is perfonned with anapplied voltage sufficiently small that the major electrolyteconstituents do not take part in either electrode reaction and theimpurities are not deposited at the cathodes.

Although any of the aforementioned methods of introducing a copperfluoride equivalent into the molten copper may be used in the process ofthis invention. for the purposes of the remainder of the discussion inthis specification it will be assumed that copper fluoride wasintroduced as anhydrous copper fluoride.

The stoichiometry of the copper fluoride changes as it becomes saturatedwith copper metal until it attains the composition range of from aboutCuF to about CuF depending upon the temperature employedv The copperfluoride is largely immiscible in the liquid copper, and because of itslower density forms a slag or salt phase above the molten metal.

The refining reactions occur because of the favorable ther modynamicproperties of copper fluoride as compared with the thermodynamicproperties of the impurity element fluorides. More specifically theGibbs free energy of formation is thought to be substantially lessnegative than for the formation ofthe fluorides of the impurityelements.

The following typical reactions are believed to occur spontaneously inthe molten copper when copper fluoride is introduced therein.

CuF,+Fe (dissolved in liquid Cul-v FeF,( l )+Cu( l CuF,+Ni (dissolved inliquid Cu) NiF (1)+Cu(l) CuF 2/3Bi (dissolved in liquid Cu 2/3BiF l)+Cu( 1) CuF +/3As (dissolved in liquid Cu)-+AsF,(g)+Cu( l) Analternative formalism which can be used in writing the reactions whereCuF is used is: (2/.r)CuF,+Fe (dissolved in liquid Cu)- FeF,( l)+2/.tCu( i) Information in the literature on standard free energies offormation of inorganic fluorides is neither extensive nor reliable. noris thermodynamic activity data for the above noted species availableexcept in a few cases, so it is not possible to predict in advance.through routine knowledge of the literature and the state-of-the-art ofchemical process metallurgy, that all metallic and nonmetallicimpurities can be converted to fluorides by reaction with copperfluoride to an extent which makes these reactions useful for refiningcopper.

It has been experimentally found that when a charge of impure liquid ormolten copper and cupric fluoride contact each other that the metallicimpurities in the copper are rapidly and completely transferred to thesalt phase. These impurities that have been transferred to the saltphase may be classified into two groups: (1 those impurities whosefluorides are volatile at the temperatures of the reaction andimmediately escape as gases from the salt phase (such as arsenic,antimony. and tin) and (2) those impurities which are essentiallynonvolatile and tend to remain in the salt phase such as nickel. iron.lead, and bismuth. The significance of this classification is that theimpurities forming the volatile fluorides (a) do not accumulate in thesalt phase and thus do not lead to the requirement for a saltrepurification process, and (b) tend not to require as negative a freeenergy of reaction with copper fluoride as impurities formingnonvolatile fluorides, because the thermodynamic activities of thevolatile impurity fluoride species are suppressed and held to a lowlevel by their evaporation from the salt The following examples 2through 5 illustrate the removal of the metallic impurities from moltencopper. In these experi- TABLE V.-ANALYSES Weight percent Example 2Example 3 Example 4 Example 5 Starting "blister" Metal Salt Metal SaltMetal Salt Metal Salt 041 00040 1159 00032 304 00074 150 000-18 168 0110001 .053 .00034 .100 0001 .057 .0003-l .061 .019 .0001 .183 .0001 .220.0001 .115 (.0001 .084 .0016 .00001 .0036 .0000l .0028 (00001 .000300001 .0007 .081 0002 .000l 0002 .0003 0002 .0003 .0002 .0003 013 .0004.0003 .0003 .0001 0003 0001 (.0003 2 0097 27. 98 0084 26. 92 0006 27. 520070 21'. B81. Bal 70. 97 Ba]. 70. 45 B31 70. ll? B81 71. 34

ments a charge of impure molten copper was allowed to contact copperfluoride at l.l C. under an inert atmosphere in a graphite crucible.After sufficient time for reaction the crucible contents were cooled andthe products analyzed. Table V below presents impurity analyses of theinitial metal and the products of each of the examples. 003000 It issignificant that the same degree of metal purification was achieved inthese four examples despite a deliberate variation in experimentalparameters as shown by table VI:

it is noteworthy that the metal product in the above examples iscomparable in purity level to conventional electrolytic cathode gradecopper after only a single stage of contact with copper fluoride.

In some cases the initial impurity level of the molten copper may bemuch higher than in the above examples. For highly contaminated blisteror scrap copper, two or more stages of reaction with copper fluoride maybe necessary in order to obtain the desired impurity level.

Example 6 This example illustrates equilibrium at high impurityconcentrations. The data was obtained by isolation of the two liquids,i.e. the liquid metal phase and the liquid salt phase at 1.091 C. Theanalyses shown below were confined to the nonvolatile impurities such asnickel, iron. lead and bismuth since these metal impurities tend toaccumulate in the salt phase and must eventually be removed bypurification. Table Vll shows that the ratio of impurity concentrationin the salt phase (B) to that in the metal (A) is very high. It can beextrapolated from this data that most impure coppers can be refined bythe process of the present invention with no more than two stages ofcontact by copper fluoride.

TABLE Vll Equilibrium Compositions at High Impurity Level A. Metal Phase8. Salt Phase Ratio BIA (Analyses in Weight Percent) Ni 0.0074 2.30Jlll.

F: 00008 1.47 ll.

Pb 0.0024 L46 006.

Hi 0.00002 0.693 3.5 tl0 An important consideration in the process ofcopper fluoride refining is the nature of the CuF Cu phase diagram. andmore specifically the solubility of salt in the metal phase as theprocess temperature is raised above the monotectic point (the lowesttemperature at which the copper metal is liquid). It has been foundexperimentally that the solubility of salt in the metal phase isextremely small in the temperature range of interest. For example atl.l28 C. the solubility of copper fluoride in molten copper is 522 partsper million by weight. At the monotectic temperature. L083 C.. diesolubility of copper fluoride in molten copper is 105 parts per millionby weight. Because of the nature of the experimental method indetermining these values they are regarded to be the upper limit ofsolubility so that the true values will be smaller.

Example 7 This is an example of the use of copper fluoride in dilutedform. A charge comprising 20 mole percent copper fluoride.

balance CaF -MgF, eutectic mixture. was reacted with molten impurecopper at Ll I4 0. for 2 hours. The results of this experiment are shownin table VIII below.

TABLE Vlll IMPU RITY ANALYSES Product Initial Metal EquilibriumCompositions Impurity Content Metal Phase Sult Phase Weight Weight iWeight i Fe 0.04) 0.00026 0046 Ni (LOSI 0.09025 004 Pb [1.[34 0.00076Ill-l1 Sh (JIMI 0.00015 0.01

Example 8 A charge comprising 5 mole percent copper fluoride in aCaF,MgFB2 eutectic mixture was reacted with molten impure copper at l. II4 C. for 2 hours. The refining results are shown in table IX below.

This example shows that a significant amount of refining is possiblewhen the nonvolatile impurity metal content of the copper is muchgreater than normally found in copper sources. A charge comprising 10mole percent copper fluoride in a CaF,MgF, eutectic mixture was reactedwith molten impure copper for 3 hours at 1.1 14 C.

TABLE X.IMPURITY ANALYSES Impurity Analysis of product Ratios content.Initial wt. Metal. wt. Salt. wt. Impurity Suit metal percent percentpercent removal transfer Fe 1.0 .00031 1.65 3.2mm 5 5X) Ni.-.. 1.0 .00151.70 6.7)(10 1.1)(10 Pb 1.0 .00037 1.53 2.7X1U 4.1)(10 Bi 1.0 .00044.066 2.3)(10 1 6X10 See the l'ollowing ratios:

Impurity removal ratio =weight percent impurity in initial metal weightpcrc nt impurity in product metal Salt transl r ratio =weight percent.impurity in product salt weight percent Impurity in product metal Fromobserving additional experiments using stable salt solvents as diluentscontaining from about 1 to 20 or more mole percent of copper fluoride ina salt mixture and various temperatures, time of reaction. types ofimpurities and concentration of impurities it can be concluded that (a)refining reactions are relatively rapid; (b) 5 mole percent of a copperfluoride in the salt charge is very nearly as effective as mole percentcopper fluoride; (c) sulfur and tellurium are not removed by thefluoride refining reaction so that the first step of anionic impurityremoval should be employed as part of an overall refining process; and(d) the effect of increased temperature is adverse but not unduly sothus permitting a latitude of at least 50 C. above the melting point ofcopper in the choice of operating temperature.

The practical utility of a high-temperature metal refining process suchas the one described in this application is very much dependent on theavailability of suitable materials of construction for containment ofmetal, salt, and vapors which arise as products or are introduced asreactants. I have found that graphite and carbon are excellent materialsfor containment, and graphite for electrode leads. As an anode incathodic electrolysis. the types of consumable carbon electrodes used inaluminum reduction appear to have merit. Depending on the saltcomposition present, certain oxide and silicate refractories areconsidered to be adequate. Finally, solidified salt may be employed asan insulating and sealing material, by proper engineering design of heatremoval from the apparatus, much as frozen cryolite has proven to be thebest insulator in aluminum reduction cells.

The engineering design of chemical reaction vessels for the process willemphasize certain criteria, among which are providing a high ratio ofreactive surface to volume, by dispersing metal droplets in the saltphase or salt droplets in the metal phase, or bubbles of reactant vaporin the metal phase or in the salt phase. A second criterion is theprovision of a more or less sealed vessel, such that moisture and otherhydrogen sources are excluded and oxygen is restricted to lowconcentrations. While inert gases such as nitrogen and argon aresuitable as gas blankets in the apparatus, I believe that less costlyprotective atmospheres will suffice. Depending on the particularselection of impurity metals present and the fluorine potential in theapparatus. it may sufl'lce to use dried air as a protective atmosphere;alternately dried combustion gases containing no hydrogen may be used,such as a mixture of CO, and CO.

There are two optional sequences in time by which the two steps of themetal refining process of this application may be conducted, and eachhas its own apparent special advantages. in the first optional methodthe two steps are conducted separately, with anion impurity removalpreceding metal impurity removal. in the second method, the two stepsare conducted simultaneously in one electrochemical reactor. Thisreactor comprises two complete electrolytic cells, having as a commonelectrode the impure liquid copper which serves as cathode of one celland anode of the other. It is maintained at an electrical potentialintermediate between the end anode, at which 0,8,, Se,, Te, may bedischarging, and the end cathode at which copper metal and/or impuritymetals are deposited. it is desirable to keep the two electrolytesphysically separated into an anion removal section and a cation removalsection.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or the essential characteristicsthereof. The embodiments presented above are therefore to be consideredas in all respects illustrative and not restrictive, the scope of theinvention being indicated by the appended claims, and all changes whichcome within the meaning and range of equivalency are intended to beembraced therein.

What is claimed is:

l. The process of removing chalcogens from molten copper comprisingmaking the molten copper the cathode of an operating electrolytic cellcontaining an electrolyte selected from the group consisting of alkalineearth chlorides, alkaline earth fluorides and mixtures thereof andpassing an electfic current through the electrolytic cell between saidcathode and an anode whereby said chalcogens are transferred from themolten copper.

2. The process of claim 1 wherein the electrolyte consists essentiallyof from about 0.3 to about 10 weight percent alkali metal halides, thebalance of the electrolyte selected from the group consisting ofalkaline earth chlorides, alkaline earth fluorides and mixtures thereof.

3. The process of claim 1 wherein the electrolyte is selected from thegroup consisting of calcium chloride, barium chloride, calcium fluoride,and magnesium chloride.

4. The process of refining copper comprising the steps of a. feedingimpurity-containing liquid copper to an electrolytic cell containing anelectrolyte b. passing an electric current between an anode and acathode through said electrolyte such that the liquid copper is thecathode whereby the anion-forming elements are transferred from theliquid copper cathode to the electrolyte, and reacting the liquid copperwith copper fluoride equivalent to remove the metallic impurities.

5. The process of claim 4 wherein the anion-forming elements transferredfrom the liquid copper cathode to said electrolyte are oxidized at theanode to the elemental state and discharged from the electrolytic cellas a gas.

6. The process of claim 4 wherein anion-forming elements transferredfrom the liquid copper cathode react with metallic ions of saidelectrolyte forming compounds which precipitate in said electrolyte;including the step of periodically removing the precipitated compoundsfrom said electrolyte.

7. The process of claim 4 wherein the anion-forming elements transferredfrom the liquid copper cathode react with metallic ions of saidelectrolyte forming compounds soluble in said electrolyte; including thestep of purifying said electrolyte by withdrawing a portion of saidelectrolyte from said cell, cooling said electrolyte to precipitate saidcompounds, removing said compounds from said electrolyte and returningthe purified portion of said electrolyte to said cell.

8. The process of claim 4 wherein the electrolyte is selected from thegroup consisting of alkaline earth chlorides, alkaline earth fluoridesand mixtures thereof.

9. The process of claim 8 wherein the electrolyte consists essentiallyof from about 0.3 to about 10 weight percent alkali metal halides, thebalance of the electrolyte selected from the group consisting ofalkaline earth chlorides. alkaline earth fluorides and mixtures thereof.

10. The process of claim 4 wherein the copper fluoride equivalent isselected from the group consisting of cupric fluoride, fluorine gas,fluorocarbon gas mixture, antimony pentafluoride, stannic fluoride andCuF, where is from about 0.90 to about l .50.

H. The process of claim 10 wherein the copper fluoride equivalent isdissolved in a salt solvent selected from the group consisting ofalkaline earth fluorides and mixtures thereof.

12. The process of refining copper comprising the steps of:

a. reacting liquid copper containing impurities with a solution of areactive metal dissolved in a molten salt to remove the anionicimpurities, feeding the liquid copper to an electrolytic cell such thatthe liquid copper is the anode, the electrolytic cell containing anelectrolyte selected from the group consisting of alkaline earthfluorides and mixtures thereof, the electrolyte containing at least lmole percent of a copper fluoride equivalent, and passing an electriccurrent through the cell between the liquid copper anode and a cathodewhereby the metallic impurities are transferred from the liquid copperanode to the electrolyte.

13. The process of claim 12 wherein the copper fluoride equivalent isselected from the group consisting of cupric fluoride, fluorine gas,fluorocarbon gas mixture, antimony pentafluoride, stannic fluoride andCuF, where .r is from about 0.90 to about 1.50.

14. The process of claim 13 CaF -MgFBZ eutectic mixture.

IS. The process of refining copper comprising the steps of a. feedingimpurity containing liquid copper to a first electrolytic cellcontaining a first electrolyte b. passing an electric current between ananode and a cathode through said first electrolyte such that the liquidcopper is the cathode whereby the anion-forming elements are transferredfrom the liquid copper cathode to said first electrolyte,

. feeding the anion-free liquid copper to a second electrolytic cellsuch that the liquid copper is the anode. said second electrolytic cellcontaining a second electrolyte selected from the group consisting ofalkaline earth fluorides and mixtures thereof, said second electrolytecontaining at least I mole percent of a copper fluoride equivalent andd. passing an electric current between the liquid copper anode and acathode through said second electrolyte whereby the metallic impuritiesare transferred from the liquid copper anode to said second electrolyte.

16. The process of claim 15 wherein anion-forming elements transferredfrom the liquid copper cathode to said first electrolyte are oxidized atthe anode to the elemental state and discharged from said firstelectrolytic cell as a gas.

l7. The process of claim 15 wherein anion-forming elements transferredfrom the liquid copper cathode react with metallic ions of said firstelectrolyte forming compounds wherein the electrolyte is a 16 whichprecipitate in said first electrolyte; including the step ofperiodically removing the precipitate compounds from said firstelectrolyte.

ii. The process of claim 15 wherein the anion-fonning elementstransferred from the liquid copper cathode react with metallic ions ofsaid first electrolyte forming compounds in said first electrolyte;including the step of purifying said first electrolyte by withdrawing aportion of said first electrolyte from said first cell, cooling theportion of said first electrolyte to precipitate the compounds. removingthe compounds from said first electrolyte and returning the purifiedportion of said first electrolyte to said first cell.

[9. The process of claim 15 wherein said first electrolyte is selectedfrom the group consisting of alkaline earth chlorides, alkaline earthfluorides, and mixtures thereof.

20. The process of claim 19 wherein said first electrolyte consistsessentially of from about 0.3 to about 10 weight percent alkali metalhalides, the balance of the electrolyte is selected from the groupconsisting of alkaline earth chlorides. alkaline earth fluorides andmixtures thereof.

2|. The process of claim 15 wherein the copper fluoride equivalent isselected from the group consisting of cupric fluoride, fluorine gas,fluorocarbon gas mixture, antimony pentafluoride, stannic fluoride and(IuF, where .r is from about 0.90 to about L50.

22. The process of claim 2| wherein said second electrolyte is aCaF,MgF, eutectic mixture.

CERTIFICATE OF CORRECTION Patent No. 3, 615

Inventor(s) Philip E. Lapat It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 4, 0. 034 conveniently 6 line 3, a

"CaF -MgFB2)" should read Cal? 6, delete "003000" and start Column 12,line 31,

-- lines 44-47,

as follows:

Fe Ni Pb Bi AS Sb Column 12, lines 66-69,

as follows:

-- Impurity Removal Column 15, line NXXX UNITED STATES PATENT OFFICEDated Octobpr )5 1071 line 37, in Table III, "0.0341" should read Column7, line 34, cancel "CuFg" and insert line 45, "a should read a uF .3 2should read a Column 9, line 51,

Column 11, line a new paragraph, "CaF -M FB2" should read CaF -MgR,

in Table IX, first two columns should read Impurity Content Weight 0.049.061 .134 .043 .045 .041 in Table X last tWO olumns should read SaltTransfer 10; 5.5 x 10 10 1.1 x 10 10 4.1 x 10 10 1.5 x 10 "It issignificant. 7

2, (claim 14) "CaF -MgFB2 should read Signed and sealed this 1st day ofMay 1973.

(SEAL) Attest:

EDWARD M .FLETCHER,JR. Attesting Officer ROBERT GO'I'TSCHALKCommissioner of Patents

2. The process of claim 1 wherein the electrolyte consists essentiallyof from about 0.3 to about 10 weight percent alkali metal halides, thebalance of the electrolyte selected from the group consisting ofalkaline earth chlorides, alkaline earth fluorides and mixtures thereof.3. The process of claim 1 wherein the electrolyte is selected from thegroup consisting of calcium chloride, barium chloride, calcium fluoride,and magnesium chloride.
 4. The process of refining copper comprising thesteps of a. feeding impurity-containing liquid copper to an electrolyticcell containing an electrolyte b. passing an electric current between ananode and a cathode through said electrolyte such that the liquid copperis the cathode whereby the anion-forming elements are transferred fromthe liquid copper cathode to the electrolyte, and c. reacting the liquidcopper with copper fluoride equivalent to remove the metallicimpurities.
 5. The process of claim 4 wherein the anion-forming elementstransferred from the liquid copper cathode to said electrolyte areoxidized at the anode to the elemental state and discharged from theelectrolytic cell as a gas.
 6. The process of claim 4 whereinanion-forming elements transferred from the liquid copper cathode reactwith metallic ions of said electrolyte forming compounds whichprecipitate in said electrolyte; including the step of periodicallyremoving the precipitated compounds from said electrolyte.
 7. Theprocess of claim 4 wherein the anion-forming elements transferred fromthe liquid copper cathode react with metallic ions of said electrolyteforming compounds soluble in said electrolyte; including the step ofpurifying said electrolyte by withdrawing a portion of said electrolytefrom said cell, cooling said electrolyte to precipitate said compounds,removing said compounds from said electrolyte and returning the purifiedportion of said electrolyte to said cell.
 8. The process of claim 4wherein the electrolyte is selected from the group consisting ofalkaline earth chlorides, alkaline earth fluorides and mixtures thereof.9. The process of claim 8 wherein the electrolyte consists essentiallyof from about 0.3 to about 10 weight percent alkali metal halides, thebalance of the electrolyte selected from the group consisting ofalkaline earth chlorides, alkaline earth fluorides and mixtures thereof.10. The process of claim 4 wherein the copper fluoride equivalent isselected from the group consisting of cupric fluoride, fluorine gas,fluorocarbon gas mixture, antimony pentafluoride, stannic fluoride andCuFx where x is from about 0.90 to about 1.50.
 11. The process of claim10 wherein the copper fluoride equivalent is dissolved in a salt solventselected from the group consisting of alkaline earth fluorides andmixtures thereof.
 12. The process of refining copper comprising thesteps of: a. reacting liquid copper containing impurities with asolution of a reactive metal dissolved in a molten salt to remove theanionic impurities, b. feeding the liquid copper to an electrolytic cellsuch that the liquid copper is the anode, the electrolytic cellcontaining an electrolyte selected from the group consisting of alkalineearth fluorides and mixtures thereof, the electrolyte containing atleast 1 mole percent of a copper fluoride equivalent, and c. passing anelectric current through the cell between the liquid copper anode and acathode whereby the metallic impurities are transferred from the liquidcopper anode to the electrolyte.
 13. The process of claim 12 wherein thecopper fluoride equivalent is selected from the group consisting ofcupric fluoride, fluorine gas, fluorocarbon gas mixture, antimonypentafluoride, stannic fluoride and CuFx where x is from about 0.90 toabout 1.50.
 14. The process of claim 13 wherein the electrolyte is aCaF2-MgF2 eutectic mixture.
 15. The process of refining coppercomprising the steps of a. feeding impurity containing liquid copper toa first electrolytic cell containing a first electrolyte b. passing anelectric current between an anode and a cathode through said firstelectrolyte such that the liquid copper is the cathode whereby theanion-forming elements are transferred from the liquid copper cathode tosaid first electrolyte, c. feeding the anion-free liquid copper to asecond electrolytic cell such that the liquid copper is the anode, saidsecond electrolytic cell containing a second electrolyte selected fromthe group consisting of alkaline earth fluorides and mixtures thereof,said second electrolyte containing at least 1 mole percent of a copperfluoride equivalent and d. passing an electric current between theliquid copper anode and a cathode through said second electrolytewhereby the metallic impurities are transferred from the liquid copperanode to said second electrolyte.
 16. The process of claim 15 whereinanion-forming elements transferred from the liquid copper cathode tosaid first electrolyte are oxidized at the anode to the elemental stateand discharged from said first electrolytic cell as a gas.
 17. Theprocess of claim 15 wherein anion-forming elements transferred from theliquid copper cathode react with metallic ions of said first electrolyteforming compounds which precipitate in said first electrolyte; includingthe step of periodically removing the precipitate compounds from saidfirst electrolyte.
 18. The process of claim 15 wherein the anion-formingelements transferred from the liquid copper cathode react with metallicions of said first electrolyte forming compounds in said firstelectrolyte; including the step of purifying said first electrolyte bywithdrawing a portion of said first electrolyte from said first cell,cooling the portion of said first electrolyte to precipitate thecompounds, removing the compounds from said first electrolyte andreturning the purified portion of said first electrolyte to said firstcell.
 19. The process of claim 15 wherein said first electrolyte isselected from the group consisting of alkaline earth cHlorides, alkalineearth fluorides, and mixtures thereof.
 20. The process of claim 19wherein said first electrolyte consists essentially of from about 0.3 toabout 10 weight percent alkali metal halides, the balance of theelectrolyte is selected from the group consisting of alkaline earthchlorides, alkaline earth fluorides and mixtures thereof.
 21. Theprocess of claim 15 wherein the copper fluoride equivalent is selectedfrom the group consisting of cupric fluoride, fluorine gas, fluorocarbongas mixture, antimony pentafluoride, stannic fluoride and CuFx where xis from about 0.90 to about 1.50.
 22. The process of claim 21 whereinsaid second electrolyte is a CaF2-MgF2 eutectic mixture.